1. Field of the Invention
The present invention relates generally to high temperature polymers. It relates particularly to a semi-interpenetrating polymer network approach to the obtainment of tougher and more microcracking and solvent resistant high temperature polymers particularly adapted for use as moldings, adhesives and composite matrices, and to methods of making the same.
2. Description of the Related Art
The need for lightweight components for use in the 200.degree. to 300.degree. C. range in aircraft, aerospace and electronic technologies has stimulated the development of high performance polymers. Materials used in these environments should exhibit a variety of physical and mechanical properties, which include processing ease, damage tolerance, microcracking resistance, strength, moisture and solvent resistance and thermo-oxidative stability. Although polymers presently exist that exhibit one or more of the above properties, these materials are generally deficient in at least one other desired property.
For instance, the bismaleimide polymer system has been generally the matrix material of choice for fabricating high performance polymer composites. However, it is extremely brittle due to its highly crosslinked network structure. Similarly, PMR-15, the leading commercial high temperature matrix resin, also suffers the lack of damage tolerance and microcracking resistance. Composite materials based on conventional high temperature thermoplastics, such as LaRC-TPI, polyimidesulfone and NR-150B2 are also deficient in one or more desired properties such as flow properties.
St. Clair et. al. (U.S. Pat. No. 4,695,610) and others have developed semi-interpenetrating polymer network (semi-IPN) polyimides from easy-to-process but brittle thermosetting polyimides and tough but difficult-to-process thermoplastic polyimides. However, none of these prior art products have the desired combination of properties set forth hereinabove.
Accordingly, there is a continual search in the art for high temperature polymers exhibiting improved properties, especially for aerospace structural applications.